Magnetically actuated switching device having eddy current reducing means



Oct. 26, 1965 T. F. LYON ETAL 3,214,711

MAGNETICALLY ACTUATED SWITCHING DEVICE HAVIN EDDY CURRENT REDUCING MEANS Filed June 15, 1961 INVENTORS Thomas F. Lycm George J. Sflucum ATTORNEYS United States Fatent Ofiiice 3,214,711 Patented Get. 26, 1965 3,214,711 MAGNETICALLY ACTUATED SWlTCi-IHNG DE VICE HAVING EDDY CURRENT REDUEING MEANS Thomas I Lyon and George I. Slocum, Dailas, Tern, assignors to Texas Instruments Incorporated, Dailas, Tern, a corporation of Delaware Filed June 15, 1961, Ser. No. 117,339 3 Claims. (Cl. 333-4) This invention relates to microwave phase-shifting apparatus and more particularly to a microwave phase shifter adapted for operation at very high switching speeds.

In microwave-switching apparatus, it is common to utilize a ferrite-type, magnetic flux-responsive, phase-shifting material positioned within a segment of waveguide. Switching is accomplished by applying a variable or reversible magnetic field across this material by a suitable magnetic circuit. When it is attempted to drive the magnetic circuit of such an arrangement at very high switching rates problems are encountered due to long time con stants and large switching current requirements caused by the high reluctance flux path resulting from the wide air gap across the waveguide and ferrite-type material and from eddy currents which are induced in the conductive portions of the waveguide upon a change in magnetic flux. Eddy current paths in the waveguide have the same efiect as shorted secondary turns on the magnetic circuit and so increase the reactance thereof and tend to oppose any change of flux, thereby reducing the rise rate of the magnetic circuit and rendering the switch ineffective for high speeds. These problems can be substantially re duced by utilizing thin foil walls for the waveguide portion of the switch and positioning the magnetic pole pieces in contact therewith as set forth in the copending application Serial No. 752,933, filed August 4, 1958, and assigned to the assignee of the present invention.

However, additional difficulties are encountered when a segment of double waveguide is used as set forth in the above-mentioned copending application. When a switch of the type using double waveguide is connected between a pair of double-waveguide coupling elements, then a shorted turn on the magnetic circuit of the switch is formed, since the two adjacent segments of waveguide of the switch are connected together at their ends by the waveguide-coupling elements. It is therefore necessary to electrically isolate the two adjacent sections of waveguide from each other and from the coupling elements.

In accordance with this invention, a pair of adjacent and parallel waveguide sections in a single microwave switch assembly are insulated from one another due to the fact that the waveguides are formed of a thin conductive foil attached to an insulating material. The sections of foil waveguide are isolated from the coupling segments on either end by insulating gaskets so that there is no conductive path between the two foil waveguides or between the foil waveguides and the coupling segments. In order to avoid radiation losses through the gaps caused by the insulating gaskets, and also to prevent standing waves or other effects of a discontinuity in the transmission path, shorted-end quarter-wave stub slots may be provided surrounding the gaps.

It is a principal object of this invention to provide an improved microwave switching device utilizing ferritetype phase-shifting elements mounted within a waveguide and coupled to an external source of magnetic flux. It is another object to provide a ferrite-type microwave switch adapted for operation at very high switching rates. It is a further object of this invention to provide ferrite-type microwave phase-shifting apparatus having a doublewaveguide segment and employing a reversible magnetic field which may be switched at very high rate.

Still another object is to provide a double-waveguide segment of a ferrite-type microwave switch. having insulating means to prevent electrical contact with waveguidecoupling elements on either end.

An additional object of this invention is to provide microwave-switching apparatus of the type utilizing a reversible magnetic field and having a minimum of eddy current paths which tend to restrain the change of flux through the waveguide.

Other objects and advantages of this invention will be apparent from the description which follows and from the appended claims. The invention itself may best be understood from the following description of an illustrative embodiment thereof, when read in conjunction with the accompanying drawings, in which:

FIGURE 1 is a perspective view of microwave phaseshifting apparatus utilized with this invention;

FIGURE 2 is a sectional view of the apparatus of FIG- URE 1 taken along the lines 2-2;

FIGURE 3 is an end view of a completed assembly of a microwave switch utilizing the principles of this invention;

FIGURE 4 is a side view of a portion of the microwave switch of FIGURE 3 and of a waveguide coupling attached thereto in an operative position;

FIGURE 5 is a sectional view of a portion of a microwave switch and associated microwave coupling, including a sectional view of the switch of FIGURE 3 taken along the lines 55; and

FIGURE 6 is an end view of the microwave coupling of FIGURES 4 and 5 taken along the lines 6-6 in FIG- URE 4.

With reference to FIGURES 1 and 2, there is shown a segment of double waveguide 10 including a pair of foil waveguides 11 and 12 which are positioned adjacent and generally parallel to one another. Although the waveguides are shown in greatly exaggerated thickness in FIG- URE 2 for illustrative purposes, the waveguides 11 and 12 are composed of very thin silver foil, having a thickness determined by the current penetration of the signal energy in the waveguide at the transmission frequency. The foil waveguides l1 and 12 are mounted on a plastic supporting structure 13 which is composed of a non-conductive material such as plastic. A set of ferrite-type phase-shifting elements 14 and 15 are mounted in the foil waveguides 11 and 12 on the pair of opposing H plane walls which are the broad walls perpendicular to the E-vector of the propagated wave. A magnetic core 16 is employed having opposing pole pieces 17 and 18 which are received in slots in the plastic structure 13 on opposite sides of the double waveguide segment 10, adjacent the ferrite elements l4 and 15. Surrounding some portion of the magnetic circuit of the core 16 is a winding which may include a pair of coils 2t and 21 for inducing magnetic flux therein. The direction of flux passing between the pole pieces 17 and 18 or through the ferrite elements 14 and 15 may be reversed by reversing the direction of current flow in the coil 20 and 21. Reversal of flux has the effect of changing the degree of phase shift which is imparted to microwave energy passing through the waveguides l1 and 12 by the ferrite elements 14 and 15. The coils 20 and 21 are positioned closely adjacent the plastic casing 13 rather than around the tong portion of the C-shaped core 16 for the purpose of decreasing the rise time of flux across the air gap. An illustrative microwave system in which the apparatus of FIGURES 1 and 2 may be utilized is shown in detail in the above-mentioned copending application Serial No. 752,933.

With reference to FIGURE 3, a completed microwave switching assembly is shown wherein the double-waveguide segment lii is encased in a housing 22 composed of potting resin or similar material. This housing 22 also encloses the major portion of the magnetic core 16 and the windings thereon. A silver plating 23 having a thickness of approximately .005 inch is applied to each end of the assembly, and a slit 24 is scribed or otherwise forrned in the silver plating 23 to a width of approximately .005 inch. This slit 24 is effective to electrically isolate the two foil waveguides 11 and 12 even though these guides are in contact with the silver plating 23. With this arrangement, no current can flow between the two foil waveguides 11 and 12. In order to electrically isolate the waveguides 11 and 12, along with the silver plating 23, from the waveguide couplings which must necessarily be attached to both ends of the switch device, a gasket 26 of tetrafluoroethylene, fiuorinated ethylene polymer or other similar insulating material of a thickness of approximately .005 inch is applied to each end of the assembly by cement or other suitable adhesive material.

Referring now to FIGURES 4 and 5, a microwave coupling 27 is shown attached to one end of the microwave switch assembly. The coupling 27 and a like coupling which engages the opposite end of the switch assembly include a segment of double waveguide 28 and a wide flange 29. The coupling 27 is constructed of an integral piece of conductive material and so, if this coupling were in electrical contact with both of the foil waveguides 11 and 12, then a path for eddy currents would be established. That is, the two guides 11 and 12, if shorted together at their ends, would create a conductive path which would act as a shorted secondary for the magnetic circuit of core 16. However, the gasket 26 effectively isolates the conductive coupling 2'7 from the waveguides 11 and 12. The coupling 27 is attached to the switch assembly by suitable means such as a set of bolts 30 passing through the flange 29 and including screw threads which engage threaded holes in a tableshaped member 31 which has been imbedded in the potting resin of the housing 22. The member 31 has four legs each having a threaded hole therein to receive one of the bolts 30. The member 31 has a rectangular hole in its center to clear the plastic member 13 and to insure that the member 31 is insulated from the waveguides 11 and 12. Also, the member 31 is spaced apart from the outer face of the housing 22 upon potting so that there will be no electrical contact between the plating 23 and the member 31. Of course, holes are provided in the plating 23 of a size larger than the diameter of the bolts 30 so that there is no electrical contact therewith. This arrangement avoids conductive paths between the coupling 27 and the switch assembly.

The conductive materail of the coupling 27 defines a pair of waveguides 32 and 33 which may best be seen in the end view of FIGURE 6. The guides 32 and 33 should provide a continuous path for energy being transmitted through the foil waveguides 11 and 12 of the switch assembly. In FIGURES 4 and 5, it is seen that the interposition of the gasket 26 between the coupling 27 and the switch assembly creates a gap between the waveguides 32 and 33 and the corresponding waveguides 11 and 12. Thus, in order to prevent radiation of microwave energy through these gaps, and also in order to avoid standing waves which may be established due to the discontinuity in the waveguide, a set of quarter-wave stub slots 34-37 are cast or otherwise formed in the flange 29 of the coupling 27. The depth of each of these stubs is on the order of one-quarter wavelength at the waveguide transmission frequency. The slots are formed in the conductive material of the coupling 27, and so the ends of the slots are shorted, forming shorted end quarter-wave stubs which appear at the openings thereof as very high impedances. Thus, the gaps between the waveguides 11 and 12 and the waveguides 32 and 33 appear as very low impedances, since the slots 34-37 are approximately one-quarter wavelength away from the gaps. It is noted that the slots 34-37 extend only along the long dimensions of the guides 32 and 33, the reason being that little energy will escape from the ends or short dimensions of the guides where the E-vector is at zero or a minimum.

In one embodiment of the invention, the switch is utilized with Waveguide having cross-sectional dimensions of 0.14 by 0.28 inch. The adjacent and parallel guides are spaced from one another by about 0.04 inch and the quarter-wave stub slots 34-27 are spaced from the guides by about 0.10 inch. These dimensions are suitable for waveguide frequencies of the order of 30K me. With a switch as described, it has been found that the magnitude of the driving current for the coil 20 can be reduced by a factor of about /3 and the rise time of the switching operation can be decreased from about microseconds to as little as 40 microsecond-s compared to the results obtained without the elimination of the shorted turn or, in other words, without the interposition of the insulating gasket 26 between the swich assembly and the couplings on either end.

The materials and dimensions specified above, as well as the structure of the illustrative embodiment of the invention, are given by way of example only and are not meant to be construed in a limiting sense. Various modifications of the invention will be obvious to persons skilled in the art from reading the specification, and so it is intended that the invention be limited only by the true scope of the appended claims.

What is claimed is:

1. Microwave switching apparatus comprising, in combination, first and second sections of rectangular foilwalled waveguide positioned adjacent and parallel to one another and adapted to propogate high frequency energy, said sections of waveguide being composed of thin foil mounted on the interior walls of a pair of elongated holes in a non-conductive housing such that said sections of Waveguide are insulated from one another, a magnetic core having a pair of pole pieces engaging opposite sides of both of said sections of waveguide, said pole pieces extending through said housing, a thin conductive plating on each end of said housing and contacting said sections of waveguide at the edges thereof, a narrow slit in the plating on each end of said housing running between the exposed ends of the first and second sections of waveguide, a winding surrounding said core and positioned closely adjacent said sections of waveguide, a pair of ferrite-type phase-shifting elements mounted adjacent said pole pieces within said first and second sections of waveguide, first and second coupling segments composed of integrally-connected double rectangular waveguide of size corresponding to said first and second sections of waveguide, said first coupling segment engaging one end of said first and second sections of waveguide and said second coupling segment engaging the other end of said first and second sections of waveguide, each of said coupling segments having a wide conductive flange facing said conductive plating, one of a pair of insulating gaskets positioned between said conductive plating and said wide flange of the coupling seg ment at each end of said first and second sections of waveguide and a set of quarter-wave stub slots formed in said wide flange spaced from the long sides of the openings of said double rectangular Waveguide by about one quarter wavelength at said high frequency.

2. Microwave switching apparatus comprising, in combination, first and second sections of rectangular foilwalled waveguide positioned adjacent and parallel to one another and adapted to propagate high frequency energy, said sections of waveguide being composed of thin foil mounted on the interior walls of a pair of elongated holes in a non-conductive housing that said sections of waveguide are insulated from one another, magnetic means having a pair of pole pieces engaging opposite sides of both of said sections of waveguide, said pole pieces extending through said housing, a thin conductive plating on each end of said housing and cont-acting said sections of waveguide at the edges thereof, a narrow slit in the plating on each end of said housing running between the exposed ends of the first and second sections of waveguide, ferrite-type phase-shifting means mounted adjacent said pole pieces Within said first and second sections of waveguide, first and second coupling segments with each being composed of integrally-connected double rectangular waveguide of size corresponding to said first and second sections of waveguide, said first coupling segment engaging one end of said first and second sections of waveguide and said second coupling segment engaging the other end of said first and second sections of waveguide, each of said coupling segments having a wide conductive flange facing said conductive plating, a pair of insulating gaskets, one of said insulating gaskets being positioned between said conductive plating and said wide flange of the coupling segment at each end of said first and second sections of wave-guide.

3. Microwave switching apparatus comprising, in combination, first and second sections of rectangular toilwalled waveguide positioned adjacent and parallel to one another and adapted to propagate high frequency energy, said sections of waveguide being com osed of thin foil mounted on the interior walls of a pair of elongated holes in a non-conductive housing that said sections of waveguide are insulated from one another, magnetic means having a pair of pole pieces engaging opposite sides of both of said sections of waveguide, said pole pieces extending through said housing, a thin conductive plating on one end of said housing and contacting said sections of waveguide at the edges thereof, a narrow slit in the plating on said one end of said housing running between the exposed ends of the first and second sections of waveguide, ferritetype phase-shifting means mounted adjacent said pole pieces within said first and second sections of waveguide, a coupling segment composed of integrally-connected double rectangular waveguide of size corresponding to said first and second sections of waveguide, said coupling segment engaging one end of said first and second sections of waveguide, said coupling segment having a wide conductive flange fiacing said conductive plating, and an insulating gasket positioned between said conductive plating and said wide flange of the coupling segment at said one end of said first and second sections of waveguide.

References Cited by the Examiner UNITED STATES PATENTS 2,934,725 4/ 60 Gumbrell 333-24 3,009,119 11/61 Slater 33324 3,101,458 8/63 Chandler et a1. 333-11 OTHER REFERENCES Book: Microwave Transmission Design Data, by Sperry Gyros-cope CO., 1944, pages 89 and 9-1 cited.

Ragan: Microwave Transmission Circuits, Radiation Lab. Series, Vol. 9, McGnaw-Hill, 1948. Pages 193 to 202 relied upon.

ELI LIEBERMAN, Primary Examiner.

BENNETT G. MILLER, HERMAN KARL SAALBACH,

Examiners. 

1. MICROWAVE SWITCHING APPARATUS COMPRISING, IN COMBINATION, FIRST AND SECOND SECTIONS OF RECTANGULAR FOILWALLED WAVEGUIDE POSITIONED ADJACENT AND PARALLEL TO ONE ANOTHER AND ADAPTED TO PROPOGATE HIGH FREQUENCY ENERGY, SAID SECTIONS OF WAVEGUIDE BEING COMPOSED OF THIN FOIL MOUNTED ON THE INTERIOR WALLS OF A PAIR OF ELONGATED HOLES IN A NON-CONDUCTIVE HOUSING SUCH THAT SAID SECTIONS OF WAVEGUIDE ARE INSULATED FROM ONE ANOTHER, A MAGNETIC CORE HAVING A PAIR OF POLE PIECES ENGAGING OPPOSITE SIDES OF BOTH OF SAID SECTIONS OF WAVEGUIDE, SAID POLE PIECES EXTENDING THROUGH SAID HOUSING, A THIN CONDUCTIVE PLATING ON EACH END OF SAID HOUSING AND CONTACTING SAID SECTIONS OF WAVEGUIDE AT THE EDGES THEREOF, A NARROW SLIT IN THE PLATING ON EACH OF THE FIRST AND SECOND RUNNING BETWEEN THE EXPOSED ENDS OF THE FIRST AND SECOND SECTIONS OF WAVEGUIDE, A WINDING SURROUNDING SAID CORE AND POSITIONED CLOSELY ADJACENT SAID SECTIONS OF WAVEGUIDE, A PAIR OF FERRITE-TYPE PHASE-SHIFTING ELEMENTS MOUNTED ADJACENT SAID POLE PIECES WITHIN SAID FIRST AND SECOND SECTIONS OF WAVEGUIDE, FIRST AND SECOND COUPLING SEGMENTS COMPOSED OF INTEGRALLY-CONNECTED DOUBLE REC- 